As a resin composition for a paint which forms a coating film which has a high refractive index and is excellent in heat resistance, heat aging resistance and mechanical properties, and further excellent in chemical resistance, solvent resistance and adhesive property to a substrate, there has been proposed a resin composition for a paint composed of a graft-modified cyclic olefin-based polymer obtained by graft-polymerizing hydroxyl group-containing unsaturated compound to a cyclic olefin-based polymer and a curing agent (for example, see Patent Document 1). In addition, it has been proposed that a colored base paint (A), a clear paint (B) and a clear paint (C) are used as a paint to be used in a coating film forming method for forming a coating film which is excellent in deep feel, smoothness and image clarity so as to have a refractive index of a cured coating film of the clear paint (B) which is greater by 0.02 or more than the refractive index of the cured coating film of the clear paint (C) (for example, see Patent Document 2).
In general, a filler such as metal oxide particles has been added to a paint which is used as a raw material of a coating film in order to increase a refractive index of the coating film. However, when the filler is added to the paint, not only transparency of a coating film to be formed decreases but also it is difficult to thicken a coating film since it is concerned that the filler aggregates with one another and to uniformly disperse the filler in the paint since the filler settles down in the paint with the passage of time.
Therefore, in recent years, it has been eagerly desired to develop a clear coating composition which exhibits low colorability, has a high refractive index without use of a filler, exhibits excellent glossy feel even in the case of using a filler, and can be coated into a thick film.
In addition, a clear coating composition has been used, for example, as a paint to be used for an outer plate of a body of a motor vehicle. As a clear coating composition which is resistant to scratch and corrosion and has a long shelf life, an acid epoxy-based clear coating composition containing a polyepoxide, a polycarboxylic acid having a plurality of carboxyl groups and a polyisocyanate has been proposed (for example, see Patent Document 3). However, the acid epoxy-based clear coating composition has a disadvantage of being inferior in deep feel although the composition is excellent in transparency.
As a clear coating composition which exhibits favorable storage stability and corrosion resistance, other than the acid epoxy-based clear coating composition, there has been proposed a polyurethane-based coating composition containing a polyurethane prepolymer and polyphosphoric acid as a desiccant (for example, see Patent Document 4). However, the polyurethane-based coating composition has a disadvantage of being inferior in deep feel although the coating composition is excellent in transparency as well as the acid epoxy-based clear coating composition.
Hence, in recent years, it has been eagerly desired to develop a clear coating composition to form a coating film which is excellent in transparency and deep feel, which is hard, and which is excellent in durability.